The present invention relates to an eletrically controlled valve apparatus provided with an inlet conduit for the pressurized fluid, with an outlet conduit for a tank or equivalent in order to drain the fluid from the valve, and with an outlet conduit for an actuator proper, such as a cylinder.
In the course of the development of hydraulic elevators, certain important requirements as to their operation have been set forth, among them: a driving speed independent of the load, a stepless acceleration independent of the load, and a slow-down in both directions as well as an approaching speed likewise independent of the load. In addition to this, some manufactures have triied to reduce the amount of required electronics, for instance on grounds that the consumption of electricity should be cut down.
For example, the SE publication of application No. 367,172 introduces a solution which aims at employing two magnetic valves. The said aim is achieved, but as regards hydraulics, the result is an extremely complex valve assembly composed of magnetic valves of the simple on-off type, which either close the respective flow path, or the flow path remains completely open.
In a like manner, the valve construction introduced in the DE publication of application No. 1,268,801 fulfils the above mentioned requirements set forth for the modern technique, but does so by means of hydraulic arrangements even more complicated than in the SE publication. Among other things, the apperatus comprises two magnetic valves of the on-off type, two operating spindles, a precision spindle as well as two throttle valves and a current distributor valve. The latteris needed for driving independent of the load.
The third example is the U.S. Pat. No. 4,418,794. The valve introduced in this publication comprises three operating spindles, one of which is employed steplessly by means of an electric motor, a screw sleeve and a screw bar, as well as an on-off type magnetic valve and one pressure-controlled directional valve. Consequently, this valve arrangement is fairly complex, too, mainly owing to the large number of components of different types.
As a conclusion of the discussion of the publications referred to as representative of the prior art, it is observed that the common aim is to avoid electric components, but this leads to complicated hydraulic arrangements and a disorderly confusion in the resulting technique. None of the described apparatuses, however, is realized without electromagnetic valves, and apart from one, they are of the on-off type. Furthermore, the reducing of electronic elements on the basis that the consumption of electricity should be cut down seems poorly justified, because with complicated valves the current losses in the hydraulics are probably greater than the amount of electricity required by the electronic elements.